ABSTRACT

Interest is growing in expanding the use of the heat unit (HU) calculations of COTMAN to assist in end-of-season recommendations such as irrigation termination. Current recommendations in subsurface drip irrigated cotton are inadequate to determine the optimum timing to stop irrigation. This study was conducted to determine if crop based recommendations could be used for timing the final irrigation in subsurface drip irrigated cotton in West Texas. Treatments were made by shutting off the drip irrigation in an 8 acre zone at approximately 400, 550 and 700 Heat Units (HU) after cutout, based on 5 nodes above white flower (NAWF). Evaluations included percent open boll, nodes above cracked boll (NACB) and yield.

The three timings for irrigation termination did not affect crop maturity as measured by percent open. Only the earliest measurement of NACB revealed any difference in maturity with the 400 HU treatment having fewer NACB.

Shutting off the water early did not negatively affect yield. In fact, the 400 HU treatment had the highest final yield. However, final yield data did not make since due to the 550 HU treatment having the lowest yield.

No differences were detected between the treatments for lint and seed weights.

No advantage was gained by watering subsurface drip irrigated cotton beyond the point of 400 HU past cutout. This subject needs further investigation. Additional studies need to be conducted on when irrigation should cease in drip irrigated cotton that include the measurement of other factors in addition to HU accumulation since cutout.